Spewing shield for planar triode tubes

ABSTRACT

A planar triode tube is disclosed wherein the anode-to-grid insulator includes an inwardly protruding annular spewing shield for shielding the inside of the anode-to-grid insulator from deposit of materials spewed from the cathode, grid and other portions of the tube. The spewing shield is formed as an integral portion of the anode-to-grid insulator being of one piece unitary construction all of the same material without joints between portions thereof.

United States Patent Brunhart et al.

[451 Sept. 25, 1973 SPEWlNG SHIELD FOR PLANAR TRIODE TUBES Inventors: Werner Brunhart; Wendell G.

l-lardman, both of Salt Lake City,

Utah

Assignee: Varian Associates, Palo Alto, Calif.

Filed: Oct. 30, 1972 Appl. No.: 302,314

Related U.S. Application Data Continuation of Ser. No. lll,06l, Jan. 29, 1971, abandoned.

U.S. Cl 313/326, 313/242, 313/256,

313/334 Int. Cl H0lj 1/88, l-lOlj 19/44 Field of Search 313/239, 242, 250,

[56] References Cited UNITED STATES PATENTS 3,378,716 4/1968 Braswell et a]. 313/252 Primary ExaminerRudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Att0rneyStanley Z. Cole [57] ABSTRACT A planar triode tube is disclosed wherein the anode-togrid insulator includes an inwardly protruding annular spewing shield for shielding the inside of the anode-togrid insulator from deposit of materials spewed from the cathode, grid and other portions of the tube. The spewing shield is formed as an integral portion of the anode-to-grid insulator being of one piece unitary construction all of the same material without joints between portions thereof.

5 Claims, 3 Drawing Figures PATENTED SEP25 I975 INVENTORS WERNER BRUNHART WSE;NDELL 03mm BY AM 6% ATRNEY 1 SPEWING SHIELD FOR PLANAR TRIODE TUBES This is a continuation of application Ser. No. l I 1,061 filed Jan. 29, 1971, now abandoned.

DESCRIPTION OF THE PRIOR ART Heretofore, planar triode tubes have included the provision of a spewing shield inwardly projecting from the anode-to-grid insulator. The spewing shield serves the purpose of shielding the inside of the anode-to-grid insulator from collection of spewed cathode and grid material. Deposit of such material on the inside of the anode-to-grid insulator can cause voltage breakdown of the tube as well as producing a change in the grid-toplate capacitance and producing unwanted absorption of radio frequency energy. These effects serve to degrade the performance of the tube in use. I-Ieretofore, the spewing shield has been made of alumina ceramic and was held in position inside of a Fosterite ceramic anode-to-grid insulator by a means of a interference fit. More particularly, the anode-to-grid insulator body was made of Fosterite ceramic and the alumina ceramic spewing shield, in the shape of a washer, was inserted into the green Fosterite ceramic body. Upon firing of the Fosterite ceramic insulator, with the alumina spewing shield mounted therein, the Fosterite ceramic shrunk more than the alumina washer producing a tight interference fit between the alumina ceramic shield and the surrounding anode-to-grid insulator.

The problem with the prior art anode-to-grid insulator and spewing shield construction is that it is not applicable to planar triode tubes wherein the anode-togrid insulator is made of alumina or beryllia ceramic, as insufficient shrinkage is obtained by firing to obtain a tight interference fit with an alumina or beryllia spewing shield.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of a planar triode having an improved spewing shield structure.

In one feature of the present invention, the anode-togrid insulator of a planar triode tube includes a spewing shield structure projecting inwardly from the insulator, such spewing shield structure being a one piece composite insulator and spewing shield structure, whereby fabrication of the composite structure is facilitated.

In another feature of the present invention, the anode-to-grid insulatorand the spewing shield are both made of a material selected from the class consisting of alumina and beryllia ceramic.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, partly in section, of a planar triode incorporating features of the present invention,

FIG. 2 is a detail view ofa portion ofa prior art structure similar to that of FIG. 1 delineated by line 2-2 and depicting the prior art anode-to-grid insulator and spewing shield structure, and,

FIG. 3 is a view similar to that of FIG. 2 depicting an alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a planar triode tube 1 incorporating features of the present invention. The planar triode tube 1 is of a conventional planar triode configuration with the exception of the spewing shield, as more fully described below. Briefly, the planar triode tube 1 includes a cathode emitter assembly 2 having a planar cathode emitting surface 3, such as a planar oxide cathode, heated to thermionic emission temperature by means of a cathode heater 4 supplied with current via a pair of heater leads 5, only one of which is shown.

The heater leads 5 pass through the base portion 6 of the tube via suitable feed through insulator assemblies 7 and current and potential is applied to the heater leads 5 via a pair of pins 8 which are to be inserted into a suitable socket, not shown. The cathode assembly 2 includes an outwardly directed flange assembly 9 to which dc and rf operating potentials are applied in use.

An anode electrode structure 11 having a planar electron collecting surface 12 is axially spaced from and faced opposed to the planar cathode emitter surface 3 to collect the electrons emitted from the cathode emitter 3. The anode electrode structure 11 includes a generally cylindrical copper member 13 which is brazed at its inner periphery to the inside marginal lip ofa central aperture in the bottom of a kovar cup member 14.

A planar grid electrode structure 15 is interposed in the region between the cathode emitter 3 and the anode collecting surface 12. The grid structure 15 includes a grid ring support member 16 having a plurality of closely spaced wires 17 extending thereacross and secured at their other ends to an outwardly directed grid flange structure 18. The flange structure 18 has the grid ring 16 fixedly secured thereto, as by brazing.

A plurality of annular ceramic insulator members 19, 21 and 22 are brazed at their axial ends to the adjacent flange portions of the electrode structures to form the vacuum envelope of the tube. More specifically, cathode-to-heater insulator 19 is brazed at opposite ends to the flanged base 6 and the cathode flange 9. The gridto-cathode insulator 21 is brazed at its upper end to the grid flange 18 and at its lower end to the cathode flange 9, anode-to-grid 22 is brazed at its upper end to the kovar anode flange 14 and at its lower end to the grid flange 18. Insulators 19, 21 and 22 are preferably either alumina or beryllia ceramic sealed to the adjacent flange members 14, 18, 9 and 6 by conventional molymanganese brazing techniques.

The anode-to-grid insulator 22 includes an inwardly directed annular fin member 23 serving as a spewing shield to shield the inside surface of the anode-to-grid insulator from deposits of cathode and grid material spewed from the cathode and grid in use. Such deposits have an adverse effect upon the performance of the tube by decreasing the grid-to-anode breakdown voltage, by contributing to rf loss due to the absorption of rf energy in the lossy coating, and by increasing the capacitance between grid-and-anode.

The shield 23 serves to block a line-of-sight path from the spewing portions of the tube, such as the cathode and grid. In a typical example, the spewing shield 23 has an axial thickness of approximately 0.020 inch and extends radially inward from the side wall of the anode-to-grid insulator 22 by approximately 0.085 inch. At its inner end it closely approaches the anode sealing flange 14 and is spaced therefrom by approximately b 0.010 inch.

Spewing shield 23 is conveniently formed in the anode-to-grid insulator 22 as an integral portion thereof by forming the ceramic insulator 22 of excess wall thickness and then grinding an annular groove 24 above the fin portion 23 to define the upper side of the fin and then by grinding the bottom side of the fin to leave approximately 0.020 inch thickness to the spewing shield 23. Forming composite anode-to-grid insulator 22 and spewing shield 23 as an integral one piece construction greatly facilitates fabrication of the spewing shield 23 as contrasted with the prior art.

Referring now to FIG. 2 there is shown the prior art spewing shield structure. More particularly, an anodeto-grid annular insulator 25, as of Fosterite ceramic having a radial thickness substantially greater than that shown for insulator 22 is brazed by means of an active braze seal to a titanium anode member 26 containing a molybdenum anode insert 27. A grid ring 28 is mounted between the anode 26 and a planar cathode 29. The outer marginal edge of the grid ring 28 is brazed to a grid flange member 31 which is in-turn is brazed by means of an active metal seal to the lower end of the Fosterite anode-to-grid insulator 25.

An annular spewing shield 32 of alumina ceramic is fixedly secured within the Fosterite insulator 25 by means of an interference fit. More particularly, the spewing shield 32 is ground to the proper size and inserted within a ground ID. of the anode-to-grid insulator 25 when the Fosterite ceramic is green, i.e., has not experienced its final firing. The tube is then assembled and the Fosterite anode-to-grid insulator 25 is fired causing the Fosterite to shrink and produce a tight shrink interference fit between the spewing shield 32 and the surrounding anode-to-grid insulator 25.

The problem with this prior art construction is that it is not applicable to planar triode tube construction utilizing alumina or beryllia ceramic anode-to-grid insulator members. Attempts to braze an alumina spewing shield into an alumina anode-to-grid insulator body results in a relatively costly construction which is avoided by the integral one piece construction of FIGv 1.

In use, the planar triode tube 1 is inserted within a coaxial cavity structure generally indicated schematically by lines 36 and 37 denoting grid-to-cathode and gridto-anode coaxial cavity structures, respectively. Capacitors 38 and 39 are provided to allow independent dc operating potentials to be established between cathode, grid and anode. A tuner 41 is positioned in the coaxial cavities for tuning thereof.

Referring now to FIG. 3, there is shown an alternative composite anode-to-grid insulator 22 and spewing shield 23. In this embodiment the anode-to-grid insulator 22' is cylindrical having vertical side walls with the spewing shield 23 projecting radially inward toward the side of the anode cup 14. The anode cup 14 has a radial flange at its outer end which is sealed to the upper end of the cylindrical insulator 22'. Also in this embodiment, but not shown, the cylindrical insulator 22' extends a substantial distance below the cathodeto-anode gap to an outwardly directed grid flange which in-turn supports an axially reetrant tubular grid support cylinder 43 having the grid ring 16 mounted across the end thereof. In this embodiment, the spewing shield ring 23' is formed by an inwardly directed bulge on the inside wall of ceramic member 22. The bulge is ground to the proper thickness in the axial direction forming the spewing shield portion 23.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. In a planar triode, an anode electrode structure having a first generally planar electron collecting surface and a second surface extending axially of the tube from said first surface, a cathode electrode structure having a generally planar electron emissive surface axially spaced from and facing said planar electron collecting surface of said anode, and a generally planar grid electrode structure interposed between said planar cathode and anode surfaces, the improvement comprising: a unitary, jointless, annular electrical insulator fabricated of a material taken from the class consisting of alumina and beryllia, said insulator being hermetically sealed between said anode and grid electrodes, said insulator having at least one axial surface adjacent to said second anode surface, said insulator having a first annular groove formed therein and extending from said axial insulator surface radially outwardly to form a third generally transverse surface, said insulator having a second annular groove formed therein and extending from said axial insulator surface radially outwardly to form a fourth generally transverse surface, said third and fourth generally transverse surfaces and said axial insulator surface forming an axially thin fin for intercepting material spewed from said cathode and shielding a substantial amount of the surface of said first annular groove from material spewed from said cathode electrode, said axial insulator surface of said fin having a minimum axial length to minimize the amount of spewed material received thereon.

2. A planar triode according to claim 1, in which said axial insulator surface of said fin has a length of about 0.020 inches for minimizing the amount of spewed material intercepted by said axial surface of said fin.

3. A planar triode according to claim 1, in which said axial insulator surface of said fin is spaced about 0.010 inches from said surface for shielding substantial amount of the surface of said first annular groove from said spewed material.

4. A planar triode according to claim 1, in which said fin is formed by grinding into said unitary, jointless insulator to form said first and second annular grooves.

5. In a planar triode, an anode electrode structure adjacent one end of said tube, said anode structure having a first generally planar electron collecting surface and a second surface extending axially of the tube from said first surface, a cathode electrode structure having a generally planar electron emissive surface axially spaced from and facing said planar electron collecting surface of said anode, and a generally planar grid electrode structure interposed between said planar cathode and anode surfaces, the improvement comprising: a one-piece, annular, electrical insulator fabricated of a material selected from the class consisting of alumina and beryllia, a metal flange extending radially outward from said axial surface of the anode at the anode end of said tube, said insulator being positioned between said anode and grid electrodes with the anode end of the insulator bonded to said flange, said one-piece insulator including an axially thin integral fin extending ra- 5 axis of the tube than it dially inward toward said axially extending anode surface adjacent the electron collecting surface end of the anode, said insulator having an inner wall portion extending between said tin and said flange, and said inner wall portion being throughout its length no closer to the is adjacent said fin. 

1. In a planar triode, an anode electrode structure having a first generally planar electron collecting surface and a second surface extending axially of the tube from said first surface, a cathode electrode structure having a generally planar electron emissive surface axiAlly spaced from and facing said planar electron collecting surface of said anode, and a generally planar grid electrode structure interposed between said planar cathode and anode surfaces, the improvement comprising: a unitary, jointless, annular electrical insulator fabricated of a material taken from the class consisting of alumina and beryllia, said insulator being hermetically sealed between said anode and grid electrodes, said insulator having at least one axial surface adjacent to said second anode surface, said insulator having a first annular groove formed therein and extending from said axial insulator surface radially outwardly to form a third generally transverse surface, said insulator having a second annular groove formed therein and extending from said axial insulator surface radially outwardly to form a fourth generally transverse surface, said third and fourth generally transverse surfaces and said axial insulator surface forming an axially thin fin for intercepting material spewed from said cathode and shielding a substantial amount of the surface of said first annular groove from material spewed from said cathode electrode, said axial insulator surface of said fin having a minimum axial length to minimize the amount of spewed material received thereon.
 2. A planar triode according to claim 1, in which said axial insulator surface of said fin has a length of about 0.020 inches for minimizing the amount of spewed material intercepted by said axial surface of said fin.
 3. A planar triode according to claim 1, in which said axial insulator surface of said fin is spaced about 0.010 inches from said surface for shielding substantial amount of the surface of said first annular groove from said spewed material.
 4. A planar triode according to claim 1, in which said fin is formed by grinding into said unitary, jointless insulator to form said first and second annular grooves.
 5. In a planar triode, an anode electrode structure adjacent one end of said tube, said anode structure having a first generally planar electron collecting surface and a second surface extending axially of the tube from said first surface, a cathode electrode structure having a generally planar electron emissive surface axially spaced from and facing said planar electron collecting surface of said anode, and a generally planar grid electrode structure interposed between said planar cathode and anode surfaces, the improvement comprising: a one-piece, annular, electrical insulator fabricated of a material selected from the class consisting of alumina and beryllia, a metal flange extending radially outward from said axial surface of the anode at the anode end of said tube, said insulator being positioned between said anode and grid electrodes with the anode end of the insulator bonded to said flange, said one-piece insulator including an axially thin integral fin extending radially inward toward said axially extending anode surface adjacent the electron collecting surface end of the anode, said insulator having an inner wall portion extending between said fin and said flange, and said inner wall portion being throughout its length no closer to the axis of the tube than it is adjacent said fin. 